Climate change over the next 50 years is expected to drive a quarter of land animals and plants into extinction, according to the first comprehensive study into the effect of higher temperatures on the natural world.

The sheer scale of the disaster facing the planet shocked those involved in the research. They estimate that more than 1 million species will be lost by 2050.

The results are described as "terrifying" by Chris Thomas, professor of conservation biology at Leeds University, who is lead author of the research from four continents published today in the magazine Nature.

Much of that loss - more than one in 10 of all plants and animals - is already irreversible because of the extra global warming gases already discharged into the atmosphere. But the scientists say that action to curb greenhouse gases now could save many more from the same fate.

It took two years for the largest global collaboration of experts to make the first major assessment of the effect of climate change on six biologically rich regions of the world taking in 20% of the land surface.

The research in Europe, Australia, Central and South America, and South Africa, showed that species living in mountainous areas had a greater chance of survival because they could simply move uphill to get cooler.

Those in flatter areas such as Brazil, Mexico and Australia, were more vulnerable, faced with the impossible task of moving thousands of miles to find suitable conditions.

Birds, which had the greatest chance of escape, could in theory move to a more suitable climate but the trees and other habitat they needed for survival could not keep pace and all would die.

Professor Thomas said: "When scientists set about research they hope to come up with definite results, but what we found we wish we had not. It was far, far worse than we thought, and what we have discovered may even be an underestimate."

Among the more startling findings of the scientists was that of 24 species of butterfly studied in Australia, all but three would disappear in much of their current range, and half would become extinct.

In South Africa major conservation areas such as Kruger national park risked losing up to 60% of the species under their protection.

In the Cerrado region of Brazil - also known as the Brazilian Savannah - which covers one fifth of the country, a study of 163 tree species showed that up to 70 would become extinct. Many of the plants and trees that exist in this savannah occur nowhere else in the world. The scientists concluded that 1,700 to 2,100 of these species - between 39% and 48% of the total - would disappear.

In Europe, the continent least affected by climate change, survival rates were better, but even here under the higher estimates of climate change a quarter of the birds could become extinct, and between 11% and 17% of plant species.

One British example is the Scottish crossbill which is found nowhere else. The future climate in Scotland will be different and the birds will be unable to survive, especially with rivals from warmer climes moving in.

The crossbill would need to move to Iceland, but currently there are virtually no trees and suitable food. The scientists conclude: "It seems unlikely that the species will manage to move to Iceland."

In Mexico, studies in the Chihuahuan desert confirmed that on flatter land extinction was more likely because a small change in climate would require migrations over vast distances for survival. One third of 1,870 species examined would be in trouble and three small rodents, the smokey pocket gopher, Alcorn's pocket gopher, jico deer mouse would go the way of the dodo.

In South Africa, where many popular garden plants originate, 300 plant species were studied and more than one third were expected to die out, including South Africa's national flower, the king protea.

Commenting on the findings in Nature, two other scientists, J Alan Pounds and Robert Puschendorf, who has studied the extinction of frogs in the mountains of Costa Rica since the 1980s as a result of climate change, say their colleagues have been "optimistic".

When other factors as well as increased temperatures were taken into account the extinctions would probably be greater.

"The risk of extinction increases as global warming interacts with other factors - such as landscape modification, species invasions and build-up of carbon dioxide - to disrupt communities and ecological interactions."

So many species are already destined for extinction because it takes at least 25 years for the greenhouse effect - or the trapping of the sun's rays by the carbon dioxide, methane and nitrous oxide already added to the air - to have its full effect on the planet. Deserts, grasslands and forests are already changing to make survival impossible.

The continuous discharging of more greenhouse gases, particularly by the USA, is making matters considerably worse. The research says if mankind continues to burn oil, coal and gas at the current rate, up to one third of all life forms will be doomed by 2050.

Prof Thomas said it was urgent to switch from fossil fuels to a non-carbon economy as quickly as possible. "It is possible to drastically reduce the output of greenhouse gases into the atmosphere and this research makes it imperative we do it as soon as possible. If we can stabilise the climate and even reverse the warming we could save these species, but we must start to act now."

If conservation groups wanted to save species they should devote at least half their energies to political campaigning to reduce global warming because that was the greatest single threat to survival of the species.

John Lanchbery, climate change campaigner for the Royal Society for the Protection of Birds, agreed: "This is a deeply depressing paper. President Bush risks having the biggest impact on wildlife since the meteorite that wiped out the dinosaurs.

"At best, in 50 years, a host of wildlife will be committed to extinction because of human-induced climate change. At worst, the outcome does not bear thinking about. Drastic action to cut emissions is clearly needed by everyone, but especially the USA."